Known devices may be helpful in providing in vivo sensing, such as imaging or pH sensing. Autonomous in vivo sensing devices, such as swallowable or ingestible capsules or other devices may move through a body lumen, sensing as they move along. An autonomous in vivo sensing device such as an imaging device may include, for example, an imager for obtaining images from inside a body cavity or lumen, such as the gastrointestinal (GI) tract while the in vivo imaging device passes through the GI lumen. The imager may, for example, be associated with an optical system, and optionally a transmitter and an antenna. Some of these devices use a wireless connection to transmit image data. Other devices, systems, and methods for in vivo sensing of passages or cavities within a body, and for sensing and gathering information (e.g., image information, pH information, temperature information, electrical impedance information, pressure information, etc.), are known in the art.
Since it is important not only to obtain images of the in vivo lumen, such as those of the GI tract, but also to know where these images were taken to be able to provide effective treatment, an accurate localization of the imaging device becomes an important task. A precise presentation of the localization of the imaging device, such as a swallowable capsule, would enable the operator of the apparatus to accurately determine where the in vivo the capsule was located when the image was captured.
Localization of an item in a three dimensional (3-D) space has been addressed by various methods and solutions. Typically, the larger the entity that needs to be localized, the closer the item to the localizing system, and the stronger the source of energy used for the localization, the easier the solution for localization. Localization of an entity in a 3-D space may, typically, return a set of three coordinates, for example X, Y, and Z parameters in a Cartesian system, and a set of three orientation parameters, indicating the orientation of the item with respect to a reference frame.
Various methods and systems for localization based on an electro-magnetic field are known. Magnetic localization methods are based on the use of a magnetic source that can generate a set of prescribed magnetic field patterns in a given domain in space, and a magnetic sensor designed to “read” the magnetic field. Traditionally, the magnetic source consists of three orthogonal magnetic dipoles (current loops, or source coils) that can be excited independently by time-varying currents of frequency ω. The sensor consists of three orthogonal coils. The voltage excited across the terminal of a single sensor coil is proportional to ωH·{circumflex over (n)}, where H is the magnetic field, and {circumflex over (n)} is a unit vector normal to the coil plane. Therefore, the three orthogonal sensor coils can be used to determine the local magnetic field, i.e. its strength and its direction relative to the sensor coordinate system (for example, the coordinate system defined by the three orthogonal sensor coils). The local magnetic fields for three linearly independent excitations (the source orthogonal dipoles) provide sufficient information to determine the sensor location. This is the principle of operation in traditional magnetic localization systems. However, in many applications the physical space and/or electronic resources that can be allocated for a source and/or a sensor are extremely limited. In such cases, a magnetic localization system utilizing a single-coil source and/or sensor may be of importance. One option is to use more than one set of dipole sources and/or sensors; say N sources and/or N sensors, each with its own distinct location rn, n=1, . . . N−1 and orientation {circumflex over (v)}n, n=1, . . . N−1 relative to the pre-defined “main” source and/or sensor, conveniently situated at r0=0. If the relative locations and orientations of these N distinct sensors are known, then an algorithm for determining the location of the source coil can be derived, as described by H. C. Gilbert in “Dipole moment detector and localizer,” U.S. Pat. No. 5,731,996. The main disadvantage of this approach is the need to have a precise knowledge of rn and {circumflex over (v)}n. For example, in some medical applications it is desirable to locate the sources on the patient's body. In such a situation it may be difficult to measure their relative locations and orientations, and furthermore, these may vary in time due to patient's movements. A solution for accurate localization, which requires a small space and overcomes the drawbacks illustrated above, is thus required.